1. Field of the Invention
The present invention relates in general to radiodetermination systems and in particular, to an apparatus and method for providing radiodetermination using a system of networked ground transceivers located in known positions that, alone or with a plurality of Satellite Positioning System satellites, allows a user to precisely determine its position location, its timing, and/or its velocity.
2. Prior Art
The art of surveying involves the determination of an unknown position from angular and distance measurements taken from one or more reference positions. The Global Positioning System (GPS) is a widely used satellite-based navigational system consisting of a network of satellites broadcasting pseudo-random noise (PRN) codes modulated on an L-band carrier (L1, L2). A GPS receiver uses measurements of the PRN code-phase and carrier-phase from four or more satellites to solve for the three-dimensional position of the receiver and to calibrate its internal time reference. The GPS receiver determines velocity from measurements of the carrier phase and doppler shifts. The accuracy of a location as provided by the GPS approach is limited by the errors on the GPS signals and the geometry established by the positions of the satellites relative to the user.
For instance, there are areas of limited visibility of the sky where the user can observe and receive the satellite signals from only a limited number of Satellite Positioning System (SATPS) satellites. Thus, in such an area, it is impossible for the user to precisely solve for the three-dimensional position of its receiver, to calibrate its internal time reference, or to determine its velocity.
Moreover, there are instances where the user does not have accessibility to any of the satellites or accessibility to equipment for observing and receiving the satellite signals from the SAPTS satellites. In such instances, the user must rely on other navigational systems to precisely solve for its three-dimensional position, to calibrate its internal time reference or to determine its velocity.
Accordingly, there is a need in the technology for an apparatus and method of providing radiodetermination using a system of networked ground transmitters located in well-known positions that, alone, or together with at least one visible SATPS satellite, allows the user to precisely determine its position location, its timing, and/or its velocity.